1. Field of the Invention
The present invention relates to a tape tensioning mechanism, and more particularly to a tape tensioning mechanism for tensioning a magnetic tape in a magnetic tape recorder.
2. Description of the Prior Art
Magnetic tape recorders are required to transport a magnetic tape under a suitable tension which should be kept as constant as possible. In video tape recorders, particularly, it is important that a magnetic tape be held as stably as possible around a head drum while signals are being recorded on or reproduced from the magnetic tape. If the magnetic tape is not held under a suitable tension or is subject to tension fluctuations while it is being transported, then the magnetic tape will be wound unstably around the head drum.
Usually, the tape transport systems of magnetic tape recorders, typically video tape recorders, have a tape tensioning mechanism for keeping a magnetic tape under proper tension while it is being transported.
Many tape tensioning mechanisms comprise a tensioning pin for contacting a magnetic tape drawn out of a tape cassette when the magnetic tape has been loaded to pass through a predetermined path, an angularly movable tensioning arm which supports the pin, and a tension spring having one end coupled to the arm for urging the arm to turn in a direction to bring the pin into contact with the magnetic tape.
FIG. 1 of the accompanying drawings shows one such conventional tape tensioning mechanism, generally denoted at a.
As shown in FIG. 1, a tape cassette c placed in a video tape recorder b has a cassette case d and a pair of rotatable tape reels e, e' disposed in the cassette case d. The tape cassette c also has a magnetic tape f with opposite ends fixed to the respective tape reels e, e', the magnetic tape f being wound around the tape reels e, e'. Before a tape length between the tape reels e, e' is drawn out and loaded into a predetermined tape path within the video tape recorder b, it extends out of the cassette case d from tape outlets in opposite sides of a front face of the cassette case d and through a front recess g defined in the cassette case d.
The video tape recorder b includes a head drum h having rotary magnetic heads (not shown) movable along the outer circumferential surface thereof, and a pair of reel bases i, i' engaged by the respective tape reels e, e'. The reel base i engaged by one of the tape reels e is coupled to a brake drum j that is positioned beneath the tape base i.
The video tape recorder b also has a pair of movable guides k, k' for engaging and loading the magnetic tape f into the predetermined tape path, a pinch roller l, and a tape guide m. When the tape cassette c is inserted into the video tape recorder b, the movable guides k, k', the pinch roller l, and the tape guide m are positioned in the recess g. To load the magnetic tape f, the movable guides k, k', the pinch roller l, and the tape guide m are moved to a loading position indicated by the two-dot-and-dash lines. A certain length of the magnetic tape f is now drawn from the cassette case d into the tape path in which it is wound around the head drum h, with the pinch roller l pressing the magnetic tape f against a capstan n. The magnetic tape f can be transported along the tape path by the capstan n that is rotated at a constant speed and the pinch roller I held thereagainst.
A cylindrical tensioning pin p is mounted on one end of an angularly movable tensioning arm o whose other end is rotatably supported on a chassis (not shown) of the video tape recorder b. A resilient band q has one end fixed to the chassis and the other end coupled to the tensioning arm o at a position near the rotatably supported end thereof. The resilient band q has an intermediate portion to be wound around the brake drum j.
A tension spring s has one end engaged by a spring retainer r which is affixed to the chassis. The other end of the tension spring s engages the tensioning arm o near the resilient band g.
The tensioning arm o is normally urged to turn counterclockwise about its supported end under the tension of the tension spring s. Before the magnetic tape f is loaded into the tape path, the tensioning arm o is held in an initial position as indicated by the solid lines by the movable guide k that is positioned within the recess g.
To load the magnetic tape f, the movable guides k, k' are moved out of the recess g toward the position indicated by the two-dot-and-dash lines. The tensioning arm o is now released from the movable guide k and rotated counterclockwise under the tension of the tension spring s into a position indicated by the two-dot-and-dash lines. The tensioning pin p on the tensioning arm o is brought into resilient contact with the magnetic tape f thus loaded in a direction substantially perpendicular to the magnetic tape f. The intermediate portion of the resilient band q is now wound around the brake drum j.
The magnetic tape f is therefore tensioned by the tensioning pin p. It is assumed that the tape reel e serves as a supply reel and the tape reel e' as a take-up reel. The tape reel e' is rotated by a motor (not shown) coupled to the reel base i'. When the tension of the magnetic tape f increases while the magnetic tape f is being transported, it pushes the tensioning pin p to the right, turning the tensioning arm o clockwise thereby to loosen the resilient band q around the brake drum j. The load on the reel base i and the tape reel e as they rotate is reduced, and the angle through which the magnetic tape f is held in contact with the tensioning pin p is also reduced. Therefore, the tension which the magnetic tape f undergoes is reduced. Conversely, when the tension of the magnetic tape f decreases while the magnetic tape f is being transported, it allows the tensioning pin p to move to the left, turning the tensioning arm o counterclockwise thereby to tighten the resilient band g around the brake drum j. The load on the reel base i and the tape reel e as they rotate is increased, and the angle through which the magnetic tape f is held in contact with the tensioning pin p is also increased. Therefore, the tension which the magnetic tape f undergoes becomes larger.
Consequently, the magnetic tape f is kept under a substantially constant tension during the transport thereof along the tape path from the tape reel e to the tape reel e'.
However, the tension spring s of the conventional tape tensioning mechanism a is required to be relatively large, i.e., have a large diameter and a large number of turns. More specifically, while the tensioning pin p is held in contact with the magnetic tape f, the tension spring s is required to be slightly stretched, i.e., to store an amount of energy large enough to bias the tensioning arm o to press the tensioning pin p lightly against the magnetic tape f. In the initial state prior to the loading of the magnetic tape f, however, the tensioning arm o is displaced far away from the position it takes when the magnetic tape f is loaded. As shown in FIG. 1, the tension spring s in the initial state is considerably longer than it is when the magnetic tape f is loaded. Thus, the tension spring s is actually required to store an amount of energy large enough to rotate the tensioning arm o from the initial position indicated by the solid lines to the position indicated by the two-dot-and-dash lines, and hence to have a large diameter and a large number of turns.
The relatively large tension spring s has heretofore been one of the mechanical limitations which have prevented the tape tensioning mechanism from being reduced in size.